Men who are infertile because of defects in their semen appear to be at increased risk of dying sooner than men with normal semen, says a new study published in journal Human Reproduction.

Men with two or more abnormalities in their semen were more than twice as likely to die over a roughly eight-year period as men who had normal semen, found the study by researchers at the Stanford University School of Medicine.

Smoking and diabetes, either of which doubles mortality risk, both get a lot of attention, noted the study’s lead author Michael Eisenberg, Assistant Professor of Urology and Stanford’s Director of male reproductive medicine and surgery.

“But here we’re seeing the same doubled risk with male infertility, which is relatively understudied,” said Eisenberg.

In the new study, Eisenberg and his colleagues examined records of men aged 20 to 50 who had visited one of two centres to be evaluated for possible infertility.

In all, about 12,000 men fitting this description were seen between 1994 and 2011 at Stanford Hospital & Clinics or between 1989 and 2009 at the Baylor College of Medicine in Houston.

At both clinics, data were available for several aspects of a patient’s semen quality, such as total semen volume and sperm counts, motility and shape.

By keying identifiers for the patients to data in the National Death Index and the Social Security Death index, the investigators were able to monitor these men’s mortality for a median of about eight years.

“We were able to determine with better than 90 per cent accuracy who died during that follow-up time,” said Eisenberg.

While no single semen abnormality in itself predicted mortality, men with two or more such abnormalities had more than double the risk of death. The greater the number of abnormalities, the higher the mortality rate, the study found.